944 S2 Cold start woes

[Uncle_Badger]

Hi All,

I bought my 1989 944 S2 Cabriolet last year and have been having great fun with it.

Admittedly it is a wee bit tatty at the moment and the electric hood doesn't work but nothing some minor bodywork and respray won't sort out. I will get it into good condition as it's always been my favourite since I was a kid. Plus it is amazingly quick.

The car was given a full service including timing belts and general once-over by Phil Raby Specialist Cars after I bought it and pronounced mechanically sound which was a great relief since I'm not much of a mechanic really.

I have it stored in a dry garage and use it whenever I can sneak off and the weather is dry.

HOWEVER I went to start it today to go into town on a little errand and it just would not fire-up. Admittedly it is proper Brass Monkeys outside (currently -4.5) but I hadn't quite expected this. I am going on the basis that I haven't had to winter-start a petrol car for ages.

I tried a jump start because the battery felt weak. It turned over no worries and I can hear the fuel injector rail ticking but it never would quite fire up. It nearly got there a few times but still never started.

I am writing to ask if anyone has got any suggestions. I was wondering about the automatic choke and how I can tell whether it is in the correct setting. The starter motor is obviously turning, there isn't an immobiliser. I was contemplating trying to warm it all up somehow with a hot air gun but then scared myself that might be dangerous.

Any suggestions, perhaps excluding "Try it again in April mate", would be much appreciated.

I'm not really sure what I can actually check myself without resorting to a garage but I feel there ought to be something.

Kind regards

Gareth

 

[Uncle_Badger]

What do you mean there is no such thing as an automatic choke on the 944 and it’s all controlled by the Bosch Motronic system and DME Relay??? It’s practically modern-day Witchcraft!

Whatever will these fiendishly cunning Germans think of next…

I will make that my first port of call.

 

[Eldavo]

If the DME temperature sensor fails then it fails “open” so the car will think it‘s -40C . Cold start won’t be a problem but it will run rich when up to temperature.

I’d try jumpering the DME relay relay terminals as per the info on “Clark’s Garage” to be sure that the fuel pump is working too.

 

[scam75]

Yeah, DME relay first port of call, then probably crank sensor. Clark's has it covered as Eldavo says.

 

[nigelsclark]

If the DME relay and crank sensor don't solve it, try investigating the alarm/immobiliser. Lots of them were fitted by the dealers when supplying the cars in the UK, so wiring can vary on UK cars. I had similar starting problems on my 1990 964 C2 a while back and it was traced to the factory immobiliser. Not quite so easy to check yourself as wiring can vary from the factory diagrams. Replacement alarm modules can be found on EBay around £120 if you need one. Best of luck.

 

[Uncle_Badger]

Thanks guys I really appreciate the quick responses.

I have some detective work on my hands but this is great as I'd like to try all options before resorting to a garage.

 

[Uncle_Badger]

If the DME relay and crank sensor don't solve it, try investigating the alarm/immobiliser. Lots of them were fitted by the dealers when supplying the cars in the UK, so wiring can vary on UK cars. I had similar starting problems on my 1990 964 C2 a while back and it was traced to the factory immobiliser. Not quite so easy to check yourself as wiring can vary from the factory diagrams. Replacement alarm modules can be found on EBay around £120 if you need one. Best of luck.

Thankyou, definitely worth investigating as I can see there definitely WAS an alarm at some point because the sensors and siren are still present but I thought it was out of commission.

 

[Uncle_Badger]

If the DME temperature sensor fails then it fails “open” so the car will think it‘s -40C . Cold start won’t be a problem but it will run rich when up to temperature.

I’d try jumpering the DME relay relay terminals as per the info on “Clark’s Garage” to be sure that the fuel pump is working too.

Excellent, definitely worth a shot!! I mean, its been cold but not THAT cold so that is crucial info.

I will also try and suss-out the fuel pump, I must admit it smelt quite fuely whilst it was busy not starting and I feared it was flooded.

Many thanks for your suggestions

 

[Uncle_Badger]

Yeah, DME relay first port of call, then probably crank sensor. Clark's has it covered as Eldavo says.

Crank sensor? Wossat then? I will need to read up on this for sure. Many thanks for the steer.

 

[vitesse]

Crank sensor cables tend to get brittle with age & exposure to manifold heat over the years-they can react to careful manipulation .
-spray with GT85 ,unplug at top rear of cambox,check for verdigris in the Bosch connectors,clean if necessary ,spray with GT85,use a little vaseline when reconnecting.
it can work but check other sensible items 1st as well.

 

[Uncle_Badger]

THAR SHE BLOWS CAPN!!!

Having left the car until today due to work I replaced the DME relay with a new one and it made no difference. It is worth noting that it made no difference to the situation with either the old or the new DME relay completely removed. This supports the logic that it fails to a usable state as ElDavo advised.

Next I decided to disconnect the Bosch Motronic* ECU and give it a bench rest. Had a cup of tea, reconnected everything and turned the ignition - It Started!!

After a few brief dances of joy I remain slightly puzzled as to what has happened here but I'm assuming that in disconnecting the Bosch Motronic system it has allowed it to reset itself.

Many thanks to all contributors, all sound advice thanks!!


*NOTE: Autocorrect wants to say Moronic but that seems a bit harsh considering it is supposed to be the brains of the operation.

 

[Eldavo]

Glad to hear it’s working - for clarity its not the DME relay that fails to a useable state its the DME temperature sensor that fails open to -40 degrees C.

When the DME relay fails it usually conks out when it come sup to temperature and won’t restart until it;s cooled down again.

 

[netctl]

THAR SHE BLOWS CAPN!!!

Having left the car until today due to work I replaced the DME relay with a new one and it made no difference. It is worth noting that it made no difference to the situation with either the old or the new DME relay completely removed. This supports the logic that it fails to a usable state as ElDavo advised.

Next I decided to disconnect the Bosch Motronic* ECU and give it a bench rest. Had a cup of tea, reconnected everything and turned the ignition - It Started!!

After a few brief dances of joy I remain slightly puzzled as to what has happened here but I'm assuming that in disconnecting the Bosch Motronic system it has allowed it to reset itself.

Many thanks to all contributors, all sound advice thanks!!


*NOTE: Autocorrect wants to say Moronic but that seems a bit harsh considering it is supposed to be the brains of the operation.

I've had it on my '84 where the little rubber bung on the ECU is missing and it allows some moisture to creep its way in, I find just unplugging it and letting it warm up does the trick. I have now replaced my ECU and given it a healthy coat of contact cleaner and have not had the issue since even in -7!